I work for a synagogue, and I need an answer for the cantor here that marries people the orthodox way. The groom was married 10 years ago to a Jewish woman in a reform ceremony. He does not know where she is for the last 10 years. Does this man need to get a get from his first wife?
A woman married in a reform ceremony does not require a get. This is because the ceremony does not imply the kiddushin of the wife by the husband, but rather the exchange of rings, and the affirmative reply to the reform rabbi’s question (see Iggros Moshe, Even Ha’ezer 3:25). In addition, there were almost certainly no Torah-valid witnesses to the kiddushin (see Teshuvos Vehanhagos 4:282). There might be circumstances in which we would be stringent lechatchilah, but with regard to the man, there is no need to be stringent, and he is permitted to get married again.